Medical professionals frequently employ specula to view or dilate areas within the body. Specula are well known. The first reference to a speculum occurred in 1597 and related to a device for dilating the eyelids. A century later, oral and vaginal specula were disclosed “wherewith the womb or mouth is dilated or opened.” William A. Smellie describes in his 1752 treatise on midwifery a “speculum matricis” for spreading open the cervix to look into the womb. Nearly a century later, Robert Graves disclosed the Grave's speculum, a bivalve vaginal speculum that is still in use today. By 1862, a catalog produced at an international exhibit in Britain disclosed specula for dilating the eye, ear, vagina, rectum and nose.
These specula typically have smooth surfaces capable of slipping comfortably into and dilating a bodily orifice for viewing by a medical professional. The medical professional typically views the area of interest by looking down the center of the smooth, dilating surface, which is frequently constructed as bivalve blades, a hollow cone, or a cylinder. The inside surface of the specula are also typically highly reflective, so that light from a head light or ambient light in the room reflects off of the surface and illuminates the area of interest.
More recently, several specula useful in spinal surgery have been disclosed. The Cloward speculum, described in the 1950's, includes a rigid, hollow cylinder fixed to a perpendicular plane, or “foot”. The foot has a cut-out on the overlapping area so the view down the center of the cylinder is unobstructed. The foot also includes metal prongs. These prongs can be hammered into a cervical vertebral body to stabilize the speculum. The surgeon can then drill near affected cervical discs and insert a dowel cut from the iliac crest to distract the disc space of the affected discs.
Parviz Kambin used a two-portal speculum system for spinal surgery, with a hole on both sides of a patient's spine. In this design, a speculum dilates each hole. A surgeon “works down” one hole with surgical instruments and looks down the second hole with, for example, an endoscope to view what he or she is doing. However, one of the disadvantages of this approach is that endoscopes do not accurately indicate depth, and surgeons frequently may damage the lens of the endoscope with the surgical instruments or could damage sensitive neurological tissue by feeling around the cavity with the instruments to determine “depth of field.”
Another speculum used in spinal surgery is the Michelson speculum. It includes a rigid, hollow cylinder with teeth projecting outwardly from one end. The teeth are driven into the vertebrae adjacent to a distracted intervertebral space. The rigidity of this speculum can be a problem, however, as the size and shape of the dilation cannot be easily changed, if at all. Additionally, surgeons may use “cottonoids,” small structures the size of postage stamps with strings attached, to control bleeding. These cottonoid strings may obstruct vision inside of the Michelson speculum and are easily dislodged or snared by the passage of instruments through a rigid speculum.
A standard posterior approach to the spine with these specula entails stripping the muscles off of the back of the spine, traumatizing the muscles. Stretching and tearing of the muscles can cause inflamation and extreme pain. Sometimes up to two or three days of IV narcotic pain medication are necessary to aid such post-surgical recovery. This traditional approach to the spine results in denervation of the paraspinous muscles, which may be the reason for some residual post-surgical back pain. When muscles are denervated, they do not function normally and the biomechanical stability of the spine can be damaged. The multifidus muscle, the large muscle in the center of the back, is made in layers and attached in layers to the inferior edge of the lamina. This muscle functions inside its cylindrical fascia as a stiffener and stabilizer, supporting axial loads, and helping to control rotational and torsional movement of the lumbar spine. Damage to the multifidus muscle thus greatly weakens the structural integrity of the back.
Another disadvantage with these specula is that the specula are not held rigidly in place, either because they are manually held in place or are secured by gripping into bone or other parts of a subjects' body. Because these specula are not held rigidly in place, the specula cannot be effectively used as a reference point in techniques like image guided surgery.
Accordingly, a need exists for a new, improved surgical speculum capable of assisting a surgeon in performing spinal surgery without the above-mentioned disadvantages.